"They believe that Marty and his son Denali, were killed by an avalanche at Camp 3 on July 26 or 27."

More details would emerge in the next few days, Newton said.

"Right now, our thoughts are with the friends and family who have suffered a tremendous loss."

British mountaineer Adrian Hayes, who was climbing with Schmidt's expedition, said all of Camp Three had been wiped out by an avalanche.

"The deaths of a father and son is a tragedy in itself but compounded even further by the fact that Marty and Denali - who were great people that we all got to know very well in the close knit community of K2 Base Camp - were very well known, highly experienced and extremely strong mountaineers, the last people many would expect to be killed on a mountain."

Last year, Schmidt became the oldest New Zealander to climb to the top of Mt Everest at age 51.

In earlier blog posts, Schmidt had said he was looking forward to he and his son being the first father-son team to reach the K2 summit.

"Cutting away from the horizontal world to the vertical world has so much power and grace attached to it, that I love to journey this way many times of the year," Schmidt blogged.

"I have been doing this now for over 38 years... Can't see myself stopping anytime soon either."

Schmidt completed a climb of Everest last month, before heading to Pakistan where Denali met him to start their K2 expedition.They were accompanied by Schmidt's good friend and fellow climber Australian Chris Warner.

Last month, ten climbers were shot dead while attempting an ascent of K2 after their camp was stormed by a group of gunmen. Pakistani militant group Jundullah later took responsibility for the killings.

Since K2 was first conquered in 1954, about 280 people have succeeded in climbing it - with roughly one death for every three successful climbs.